CVE-2022-40073 in AC21
Summary
by MITRE • 09/19/2022
Tenda AC21 V 16.03.08.15 is vulnerable to Buffer Overflow via /bin/httpd, saveParentControlInfo.
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Analysis
by VulDB Data Team • 10/20/2022
The vulnerability identified as CVE-2022-40073 affects Tenda AC21 wireless router firmware version 16.03.08.15 and represents a critical buffer overflow condition within the web server component of the device. This flaw exists in the /bin/httpd binary specifically within the saveParentControlInfo function, which processes incoming HTTP requests and handles configuration data related to parental controls. The issue arises from insufficient input validation and bounds checking when processing user-supplied data through the web interface, creating a pathway for malicious actors to execute arbitrary code or cause system instability.
The technical exploitation of this buffer overflow vulnerability occurs when an attacker sends specially crafted HTTP requests to the router's web interface, specifically targeting the parental control configuration endpoint. The saveParentControlInfo function fails to properly validate the length of incoming data, allowing an attacker to overwrite adjacent memory regions in the process heap. This type of vulnerability falls under CWE-121, which describes stack-based buffer overflow conditions, and can potentially enable attackers to overwrite return addresses, function pointers, or other critical memory locations. The vulnerability is particularly concerning because it exists within a network service that is typically accessible from external networks, making it exploitable without physical access to the device.
The operational impact of this vulnerability extends beyond simple denial of service conditions, as it can potentially allow remote code execution with the privileges of the web server process. Successful exploitation could enable attackers to gain full administrative control over the router, potentially leading to man-in-the-middle attacks, DNS hijacking, or the use of the compromised device as a pivot point for attacking other devices on the local network. Network traffic could be intercepted, modified, or redirected, while the device might be used to launch further attacks against other systems. The vulnerability also creates a persistent threat vector since the affected firmware version remains active on the device until manually updated, and many users may not be aware of the need for firmware updates.
Mitigation strategies for this vulnerability should include immediate firmware updates from Tenda, which would contain patched versions of the affected httpd binary with proper input validation and bounds checking mechanisms. Network administrators should also implement network segmentation and access controls to limit exposure of these devices to untrusted networks. The use of intrusion detection systems and monitoring for unusual network traffic patterns can help identify potential exploitation attempts. Additionally, implementing secure configuration practices such as disabling unnecessary services, changing default credentials, and restricting remote access to the web interface can reduce the attack surface. This vulnerability aligns with ATT&CK technique T1059.007 for command and scripting interpreter, as exploitation could enable attackers to execute arbitrary commands on the affected device, and T1566 for spearphishing attachments, as the attack vector may involve social engineering to gain initial access to the network. Organizations should also consider implementing network access control policies and regular vulnerability scanning to identify other potentially vulnerable devices on their networks.